Direction-selective ganglion cells respond strongly to an image moving in the preferred direction and weakly to an image moving in the opposite, or null direction, and are critical for driving ocular-motor reflexes that stabilize images on the retina as we move through a visual scene. The preferred direction of direction-selective ganglion cells cluster along the cardinal directions (up, down, left and right) and the direction-selective ganglion cells sensitive to each cardinal direction are organized into mosaics such that at each point in space, each direction of motion is represented. The predominant model for the generation of direction selectivity in the retina is that a particular class of interneurons form inhibitory synapses on the null side of the dendritic tree of directionselective ganglion cells. The mechanisms that instruct the emergence of mosaics comprised of cells that receive an asymmetric distribution of inhibitory inputs during development are unknown. Our long-term goal is to determine the mechanisms that underlie the development of these two essential features of direction-selectivity - the circuits that underlie the null side inhibition and the existence of direction-selective ganglion cells mosaics. In particular, we will determine whether spontaneous retinal activity plays a critical role in the formation of these circuits. Here we propose to use a combination of state-of-the-art electrophysiological and imaging techniques to determine the age at which directional circuits are established.